1. Technical Field
The present disclosure relates to a plasma nitriding apparatus which nitrides part of a surface of a treatment object.
2. Description of the Related Art
A nitriding treatment to form a layer of a nitride compound having high hardness onto a metal surface has been known as one of surface treatments for improving abrasion resistance of the surface. Nitriding treatments are categorized broadly into a gas nitriding treatment and a plasma (ion) nitriding treatment. In the gas nitriding treatment, a nitrogen-containing gas such as ammonia gas is supplied around a treatment object. Then, the treatment object is heated and nitrogen originated from the nitrogen-containing gas is diffused on a surface of the treatment object. The diffused nitrogen is bonded to atoms on the surface whereby a layer of a nitride compound is formed. On the other hand, in the plasma nitriding treatment, a nitrogen-containing gas is supplied between an anode and a treatment object serving as a cathode. In this state, electric discharge is generated between the anode and the cathode to produce plasma. Nitrogen ions in the produced plasma collide with a surface of the treatment object, and the nitrogen ions are bonded to atoms on the surface. As a consequence, a layer of a nitride compound is formed on the surface of the treatment object (see Japanese Patent Application Laid-Open Publication No. 2011-84793).